Fast Neutron Damage in Superconducting Vanadium

Abstract

A single crystal of vanadium (resistivity ratio Γ = 450) was irradiated in the Oak Ridge Research Reactor at a temperature of 40°C for a series of fast neutron fluences. The sample was a prolate spheroid approximately 25 mm in length, with a minor diameter of about 3 mm Prior to and after each irradiation isothermal bulk magneti­zation measurements were carried out at various temperatures in the superconducting regime. The sample was also investigated in a Hartshorn mutual inductance bridge before and after each irradiation. The bridge apparatus¹ was arranged so that the sample could be excited by a sinusoidal magnetic field of adjustable frequency ω and amplitude h₀ in a superposed dc biasing field H. Both fields were parallel to the long axis of the sample. The bridge was balanced with the sample in the Meissner state, so that the output was proportional to the ac magnetic permeability and could be viewed on an oscilloscope. A lock-in amplifier at the bridge output tuned to the fundamental frequency detected signals in quadrature proportional to μ’ and μ”, the real and imaginary components of the fundamental portion of the ac permeability, which is generally nonlinear.

Research sponsored by the U.S. Atomic Energy Commission under contract with Union Carbide Corporation.